3D Capacitor and Capacitor Array Fabricating Photoactive Substrates

ABSTRACT

The present invention provides a method of fabrication and device made by preparing a photosensitive glass substrate comprising at least silica, lithium oxide, aluminum oxide, and cerium oxide, masking a design layout comprising one or more holes or post to form one or more high surface area capacitive device for monolithic system level integration on a glass substrate.

FIELD OF INVENTION

The present invention relates to creating a three-dimensional capacitor structure in a photosensitive in-glass ceramic substrate, in particular, creating capacitors and in conjunction with other passive components for filters, surge protectors and storage for electronic, microwave and radio frequencies.

BACKGROUND ART

Photosensitive glass structures have been suggested for a number of micromachining and microfabrication processes such as integrated electronic elements in conjunction with other elements systems or subsystems. Silicon microfabrication of traditional glass is expensive and low yield while injection modeling or embossing processes produce inconsistent shapes. Silicon microfabrication processes rely on expensive capital equipment; photolithography and reactive ion etching or ion beam milling tools that generally cost in excess of one million dollars each and require an ultra-clean, high-production silicon fabrication facility costing millions to billions more. Injection molding and embossing are less costly methods of producing a three dimensional shapes but generate defects with in the transfer or have differences due to the stochastic curing process.

This invention creates a cost effective glass ceramic three-dimensional capacitor structure or three-dimensional capacitor array device. Where a glass ceramic substrate has demonstrated capability to form such structures through the processing of both the vertical as well as horizontal planes either separately or at the same time to form two or three-dimensional Capacitive devices.

SUMMARY OF THE INVENTION

The present invention includes a method to fabricate a substrate with one or more, two or three dimensional capacitor devices by preparing a photosensitive glass substrate with via or post and further coating or filling with one or more conductive layer typically a metal, dielectric material and a top layer conductive layer typically a metal.

A method of fabrication and device made by preparing a photosensitive glass ceramic composite substrate comprising at least silica, lithium oxide, aluminum oxide, and cerium oxide, masking a design layout comprising one or more, two or three dimensional capacitor device in the photosensitive glass substrate, exposing at least one portion of the photosensitive glass substrate to an activating energy source, exposing the photosensitive glass substrate to a heating phase of at least ten minutes above its glass transition temperature, cooling the photosensitive glass substrate to transform at least part of the exposed glass to a crystalline material to form a glass-crystalline substrate and etching the glass-crystalline substrate with an etchant solution to form one or more angled channels or through holes that are then used in the creation of capacitive device.

The present invention provides a glass ceramics capacitive device comprising: a first glass-crystalline substrate comprising one or more electrical conduction paths in the glass-crystalline substrate, and a metal coating applied to the one or more electrical conduction paths, wherein the first glass-crystalline substrate comprises at least silica, lithium oxide, aluminum oxide, and cerium oxide; a second glass-crystalline substrate comprising: one or more second electrical conduction paths in the second glass-crystalline substrate; and a second metal coating applied to the one or more second electrical conduction paths, wherein the second glass-crystalline substrate comprises at least silica, lithium oxide, aluminum oxide, and cerium oxide; a layer of dielectric material positioned between the first glass-crystalline substrate and the second glass-crystalline substrate; and one or more via, posts, channels, or a combination thereof connecting the first glass-crystalline substrate and the second glass-crystalline substrate. The first termination may be connected to the first glass-crystalline substrate and the second termination may be connected to the second glass-crystalline substrate. The glass ceramics capacitive device may preform as a voltage storage. The metal coating, the second metal coating or both may be Au, Ag, Pt, Cu, W, TiW, TiN, TaN, WN, Al₂O₃ or mixtures and alloys thereof. The dielectric layer may be Ta₂O₅, Al₂O₃ or other vapor phase dielectrics including but not limited to Al₂O₃.

The present invention provides a method of making a capacitive device created in or on photosensitive glass ceramics comprising the steps of: providing a photosensitive glass ceramic substrate comprising at least silica, lithium oxide, aluminum oxide, and cerium oxide; masking a design layout on the photosensitive glass ceramic substrate, wherein the design layout comprises one or more structures to form one or more electrical conduction paths; exposing at least one portion of the photosensitive glass ceramic substrate to an activating energy source; heating the photosensitive glass ceramic substrate to a heating phase of at least ten minutes above its glass transition temperature; cooling the photosensitive glass ceramic substrate to transform at least part of the exposed glass to a crystalline material to form a glass-crystalline substrate; etching the glass-crystalline substrate with an etchant solution to form the one or more three dimensional etched structure in the glass-crystalline substrate; optionally converting a portion of the glass-crystalline substrate adjacent to the three dimensional etched structure to a ceramic phase; rinsing the glass-crystalline substrate with a dilute glass etchant to form a high surface area texture to glass area; coating the via or post channels with a first metal to form a bottom electrode; coating at least a portion of the structure with a dielectric media; coating the via or post channels with a second metal to form a top electrode; removing at least a portion of the top and dielectric media to provide electrical contact or free standing device; and connecting the first metal, the second metal or both to a circuitry through a surface or buried contact.

The coating of the first metal, the second metal or both uses atomic layer deposition (ALD). The glass ceramics capacitive device preforms as a voltage storage. The first metal, the second metal or both comprise Au, Ag, Pt, Cu, W, TiW, TiN, TaN, WN, Al₂O₃ or mixtures and alloys thereof. The dielectric layer may be Ta₂O₅, Al₂O₃ or other vapor phase dielectrics.

BRIEF DESCRIPTION OF THE DRAWINGS

Further benefits and advantages of the present invention will become more apparent from the following description of various embodiments that are given by way of example with reference to the accompanying drawings:

FIG. 1 Show a through hole via with 65 um diameter, 72 um center-to-center pitch.

FIG. 2 Blind via in a 1mm thick substrate where the via depth is 440 μm and the top diameter is 41 μm and bottom diameter is 19 μm

FIG. 3 Top view of high surface area and high aspect ratio devices in/on APEX® Glass

FIG. 4 Side view of filled through hole via in/on APEX® Glass

FIG. 5 Show an exploded view of a blind via with the ADL capacitor structure in color.

DESCRIPTION OF THE INVENTION

While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention.

To facilitate the understanding of this invention, a number of terms are defined below. Terms defined herein have meanings as commonly understood by a person of ordinary skill in the areas relevant to the present invention. Terms such as “a”, “an” and “the” are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration. The terminology herein is used to describe specific embodiments of the invention, but their usage does not delimit the invention, except as outlined in the claims.

To address these needs, the present inventors developed a glass ceramic (APEX®) Glass ceramic) as a novel packaging and substrate material for semiconductors, RF electronics, microwave electronics, and optical imaging. APEX® Glass ceramic is processed using first generation semiconductor equipment in a simple three step process and the final material can be fashioned into either glass, ceramic, or contain regions of both glass and ceramic. The APEX® Glass ceramic possesses several benefits over current materials, including: easily fabricated high density via, demonstrated microfluidic capability, micro-lens or micro-lens array, high Young's modulus for stiffer packages, halogen free manufacturing, and economical manufacturing. Photoetchable glasses have several advantages for the fabrication of a wide variety of microsystems components. Microstructures have been produced relatively inexpensively with these glasses using conventional semiconductor processing equipment. In general, glasses have high temperature stability, good mechanical and electrical properties, and have better chemical resistance than plastics and many metals. To our knowledge, the only commercially available photoetchable glass is FOTURAN®, made by Schott Corporation and imported into the U.S. only by Invenios Inc. FOTURAN® comprises a lithium-aluminum-silicate glass containing traces of silver ions plus other trace elements specifically silicon oxide (SiO₂) of 75-85% by weight, lithium oxide (Li₂O) of 7-11% by weight, aluminum oxide (Al2O₃) of 3-6% by weight, sodium oxide (Na₂O) of 1-2% by weight, 0.2-0.5% by weight antimonium trioxide (Sb₂O₃) or arsenic oxide (As₂O3), silver oxide (Ag₂O) of 0.05-0.15% by weight, and cerium oxide (CeO₂) of 0.01-0.04% by weight. As used herein the terms “APEX® Glass ceramic”, “APEX® glass” or simply “APEX®” is used to denote one embodiment of the glass ceramic composition of the present invention.

When exposed to UV-light within the absorption band of cerium oxide the cerium oxide acts as sensitizers, absorbing a photon and losing an electron that reduces neighboring silver oxide to form silver atoms, e.g.,

Ce³⁺+Ag⁺=□Ce⁴⁺+Ag⁰

The silver atoms coalesce into silver nanoclusters during the baking process and induce nucleation sites for crystallization of the surrounding glass. If exposed to UV light through a mask, only the exposed regions of the glass will crystallize during subsequent heat treatment.

This heat treatment must be performed at a temperature near the glass transformation temperature (e.g., greater than 465° C. in air for FOTURAN®). The crystalline phase is more soluble in etchants, such as hydrofluoric acid (HF), than the unexposed vitreous, amorphous regions. In particular, the crystalline regions of FOTURAN® are etched about 20 times faster than the amorphous regions in 10% HF, enabling microstructures with wall slopes ratios of about 20:1 when the exposed regions are removed.

Generally, glass ceramics materials have had limited success in microstructure formation plagued by performance, uniformity, usability by others and availability issues. Past glass-ceramic materials have yield etch aspect-ratio of approximately 15:1, in contrast APEX® Glass has an average etch aspect ratio greater than 50:1. This allows users to create smaller and deeper features. Additionally, our manufacturing process enables product yields of greater than 90% (legacy glass yields are closer to 50%). Lastly, in legacy glass ceramics, approximately only 30% of the glass is converted into the ceramic state, whereas with APEX™ Glass ceramic this conversion is closer to 70%.

APEX® Glass composition provides three main mechanisms for its enhanced performance: (1) The higher amount of silver leads to the formation of smaller ceramic crystals which are etched faster at the grain boundaries, (2) the decrease in silica content (the main constituent etched by the HF acid) decreases the undesired etching of unexposed material, and (3) the higher total weight percent of the alkali metals and boron oxide produces a much more homogeneous glass during manufacturing.

Ceramicization of the glass is accomplished by exposing the entire glass substrate to approximately 20 J/cm² of 310 nm light. When trying to create glass spaces within the ceramic, users expose all of the material, except where the glass is to remain glass. In one embodiment, the present invention provides a quartz/chrome mask containing a variety of concentric circles with different diameters.

The present invention includes a method for fabricating an inductive device in or on glass ceramic structure electrical microwave and radio frequency applications. The glass ceramic substrate may be a photosensitive glass substrate having a wide number of compositional variations including but not limited to: 60-76 weight % silica; at least 3 weight % K₂O with 6 weight %-16 weight % of a combination of K₂O and Na₂O; 0.003-1 weight % of at least one oxide selected from the group consisting of Ag₂O and Au₂O; 0.003-2 weight % Cu₂O; 0.75 weight %-7 weight % B₂O₃, and 6-7 weight % Al₂O₃; with the combination of B₂O3; and Al₂O₃ not exceeding 13 weight %; 8-15 weight % Li₂O; and 0.001-0.1 weight % CeO₂. This and other varied compositions are generally referred to as the APEX® glass.

The exposed portion may be transformed into a crystalline material by heating the glass substrate to a temperature near the glass transformation temperature. When etching the glass substrate in an etchant such as hydrofluoric acid, the anisotropic-etch ratio of the exposed portion to the unexposed portion is at least 30:1 when the glass is exposed to a broad spectrum mid-ultraviolet (about 308-312 nm) flood lamp to provide a shaped glass structure that has an aspect ratio of at least 30:1, and to create an inductive structure. The mask for the exposure can be of a halftone mask that provides a continuous grey scale to the exposure to form a curved structure for the creation of an inductive structure/device. A digital mask can also be used with the flood exposure and can be used to produce the creation of an inductive structure/device. The exposed glass is then baked, typically in a two-step process. Temperature range heated between of 420° C.-520° C. for between 10 minutes to 2 hours, for the coalescing of silver ions into silver nanoparticles and temperature range heated between 520° C.-620° C. for between 10 minutes and 2 hours allowing the lithium oxide to form around the silver nanoparticles. The glass plate is then etched. The glass substrate is etched in an etchant, of HF solution, typically 5% to 10% by volume, wherein the etch ratio of exposed portion to that of the unexposed portion is at least 30:1 when exposed with a broad spectrum mid-ultraviolet flood light, and greater than 30:1 when exposed with a laser, to provide a shaped glass structure with an anisotropic-etch ratio of at least 30:1.

The present invention includes an inductive structures created in the multiple via or posts of a glass-ceramic substrate, such process employing the photodefinable glass structure containing at least one or more, two or three-dimensional capacitor device. The capacitive device is formed by one via or a series of via, where the via is either through hole or blind via, a depositing a bottom electrode, dielectric, and top electrode using an atomic layer deposition (ALD) process. The via may also receive an additional low concentrated rinse, with an etchant, such as dilute HF. The dilute HF will pattern or texture the ceramic wall of the via. The texturing of the ceramic wall significantly increases to the surface area of the structure directly increasing the capacitance of the device.

The capacitive device consists of a conductive layer that adheres well to glass, a dielectric layer, a top conductive layer and a final barrier layer. The APEX® Glass dimensional structure is coated with a layer less than 2 microns of TiN or other electrode material, followed by a 2 micron or less dielectric layer of Ta₂O₅, Al₂O₃ or other vapor phase dielectrics including but not limited to Al₂O₃. Al₂O₃ at 380° C. using TMA and O₃—cycle time: 3.5 s. The Al₂O₃ layer is then heated in oxygen ambient to 300° C. for 5 min fully oxidized the dielectric layer. Then depositing a top electrode of less than 2 microns of TiN by ALD. The top and bottom electrode need to be constructed from the same material to prevent the formation of a space charge in the dielectric. Depending on the size of the work function difference the space charge may be greater than what can be overcome with an external voltage without breaking down the dielectric layer rendering the capacitor useless. Eliminating the work function issue can be achieved by the creating an ohmic contact between the electrodes and dielectric. Additional metal and insulator layers may be added to increase capacitance.

Preferred Embodiment. A preferred structure is to create a capacitor structure where the via or post has a dilute HF wash to create a high textured surface area coated TiW metallization for the bottom electrode, Tantalum pent oxide for the dielectric and TiW metallization for the top electrode. The TiW bottom electrode requires a two-step ADL process. Step one is to deposit Ti using TiCl₄ rate of 1.67 Å/cycle in about 1.8 s cycle time at a substrate temperature of 300° C. to 400° C. The second step is to deposit tungsten (W) using Si—H and W—F mixed on the substrate's surface prior to purging. A linear growth rate of W requires equal portions of each reactant during the ALD cycle. Typical ALD growth for Tungsten is 6 Å cycle, with a cycle time of 3.5 s with a substrate temperature between 177° C. to 325° C. Alternating the ALD cycle from W to Ti at the substrate temperature necessary to achieve the deposition of both metals will result in the formation of a TiW layer. The process is repeated until the TiW structure reaches 20 Å. Next a Ta₂O₅ is formed by ALD using TaCl₅ precursor in the presence of atomic hydrogen. Tantalum films are deposited at a substrate temperature of 25-400° C. with an ALD cycle time of 1.8 s. After each ALD cycle, the Tantalum films are exposed to O₂ for 30 seconds while the substrate is at 400° C. This converts the metallic Tantalum film to Ta₂O₅. The device is completed by applying a top electrode of TiW in the same manner as the bottom electrode. The very nature of ALD process enables dense conformal coatings.

Finishing the capacitor structure requires etching down to the bottom electrode so electrical connection can be made to both contacts of the capacitor. This is accomplished by coating the structure with a standard positive photoresist. Exposing the photoresist with a rectangular over part of the capacitor structure. Then developing and removing the photoresist over the capacitor exposing the top TiW photoresist electrode. The TiW electrode is etched with SF₆/He plasmas in a using a Tegal 804 plasma etching system. This etch rate with 200 W of forward power is 200 Å/min. This etch is preferentially relative to the Ta₂O₅ layer, making the Ta₂O₅ layer an effective etch stop. The Ta₂O₅ a plasma etch using Ar/Cl (10%/90%) mixture with 300 W of forward power with a 1200 Å/min etch rate. The Ar/Cl plasma does not attack/etch the TiW bottom electrode. This allows the top and bottom electrode for the capacitor to be connected to the rest of the circuit by a wide number of standard thick and thin film processes.

A second embodiment uses a through hole via that may have the ceramic phase etched with a dilute HF solution to create a textured high surface area on one side or both sides to partially or fully remove the glass-ceramic as the base substrate for the capacitive structure. A third embodiment use a posts on one or both sides of the APEX® Glass substrate that may have the ceramic phase etched with a dilute HF to create to a high surface area capacitive structure.

Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. 

1. A capacitive device created in or on photo-sensitive glass ceramics.
 2. A method of creating a capacitive device created in or on photosensitive glass ceramics consists of: preparing a photosensitive glass ceramic substrate comprising at least silica, lithium oxide, aluminum oxide, and cerium, oxide; masking a design layout comprising one or more structures to form one or more electrical conduction paths on the photosensitive glass ceramic substrate; exposing at least one portion of the photosensitive glass substrate to an activating energy source; exposing the photosensitive glass substrate to a heating phase of at least ten minutes above its glass transition temperature; cooling the photosensitive glass substrate to transform at least part of the exposed glass to a crystalline material to form a glass-crystalline substrate; etching the glass-crystalline substrate with an etchant solution to form the one or more three dimensional etched structure in the glass substrate; the glass-crystalline substrate adjacent to the three dimensionally etched structure may also be converted to a ceramic phase; rinsing with dilute glass etchant to create a high surface area texture to glass; coating the via or post channels with a metal for the bottom electrode using atomic layer deposition (ALD); coating all or part of the structure with a dielectric media using atomic layer deposition (ALD); coating the via or post channels with a metal for the top electrode using atomic layer deposition (ALD); removing all or part of the top and dielectric media to provide electrical contact or free standing device; and where the metal is connected to a circuitry through a surface or buried contact.
 3. The glass ceramics capacitive device of claim 1, wherein the glass ceramics capacitive device performs as a voltage storage device.
 4. A glass ceramics capacitive device comprising: a first glass-crystalline substrate comprising one or more electrical conduction paths in the glass-crystalline substrate, and a first metal coating applied to the one or more first electrical, conduction paths, wherein the first glass-crystalline substrate comprises at least silica, lithium oxide, aluminum oxide, and cerium oxide; a second glass-crystalline substrate comprising: one or more second electrical conduction paths in the second glass-crystalline substrate; and a second metal coating applied to the one or more second electrical conduction paths, wherein the second glass-crystalline substrate comprises at least silica, lithium oxide, aluminum oxide, and cerium oxide; a layer of dielectric material positioned between the first glass-crystalline substrate and the second glass-crystalline substrate; and one or more via, posts, channels, or a combination thereof connecting the first glass-crystalline substrate and the second glass-crystalline substrate.
 5. The device of claim 4, further comprising a first termination connected to the first glass-crystalline substrate and a second termination connected to the second glass-crystalline substrate.
 6. The device of claim 4, wherein the glass ceramics capacitive device performs as a voltage storage.
 7. The device of claim 4, wherein the first metal coating, the second metal coating or both comprise Au, Ag, Pt, Cu, W, TiW, TiN, TaN, WN, Al₂O₃ or mixtures and alloys thereof.
 8. The device of claim 4, wherein the dielectric layer comprises Ta₂O₅, Al₂O₃ or other vapor phase dielectrics including but not limited to Al₂O₃.
 9. A method of making a capacitive device created in or on photosensitive glass ceramics comprising the steps of: providing a photosensitive glass ceramic substrate comprising at least silica, lithium oxide, aluminum oxide, and cerium oxide; masking a design layout on the photosensitive glass ceramic substrate, wherein the design layout comprises one or more structures to form one or more electrical conduction paths; exposing at least one portion of the photosensitive glass ceramic substrate to an activating energy source; heating the photosensitive glass ceramic substrate to a heating phase of at least ten minutes above its glass transition temperature; cooling the photosensitive glass ceramic substrate to transform at least part of the exposed glass to a crystalline material to form a glass-crystalline substrate; etching the glass-crystalline substrate with an etchant solution to form the one or more three dimensional etched structure in the glass-crystalline substrate; optionally converting a portion of the glass-crystalline substrate adjacent to the three dimensional etched structure to a ceramic phase; rinsing the glass-crystalline substrate with a dilute glass etchant to form a high surface area texture to glass area; coating the via or post channels with a first metal to form a bottom electrode; coating at least a portion of the structure with a dielectric media; coating the via or post channels with a second metal to form a top electrode; removing at least a portion of the top and dielectric media to provide electrical contact or free standing device; and connecting the first metal, the second metal or both to a circuitry through a surface or buried contact.
 10. The method of claim 9, wherein the coating of the first metal, the second metal or both uses atomic layer deposition (ALD).
 11. The method of claim 9, wherein the glass ceramics capacitive device performs as a voltage storage device.
 12. The method of claim 9, wherein the first metal, the second metal or both comprise Au, Ag, Pt, Cu, W, TiW, TiN, TaN, WN, Al₂O₃ or mixtures and alloys thereof.
 13. The method of claim 9, wherein the dielectric layer comprises Ta₂O₅, Al₂O₃ or other vapor phase dielectrics.
 14. The device of claim 4, wherein the first metal coating, the second metal coating, or both are applied using atomic layer deposition (ALD). 